The electrophoretic display (EPD) is a non-emissive device based on the electrophoresis phenomenon of charged pigment particles dispersed in a solvent. The display typically comprises two plates with electrodes placed opposing each other. One of the electrodes is usually transparent. An electrophoretic fluid composed of a colored solvent with charged pigment particles dispersed therein is enclosed between the two plates. When a voltage difference is imposed between the two electrodes, the pigment particles migrate to one side or the other causing either the color of the pigment particles or the color of the solvent being seen from the viewing side.
Alternatively, an electrophoretic fluid may comprise two types of charged pigment particles of contrasting colors and carrying opposite charges, and the two types of the charged pigment particles are dispersed in a clear solvent or solvent mixture. In this case, when a voltage difference is imposed between the two electrode plates, the two types of the charged pigment particles would move to opposite ends (top or bottom) in a display cell. Thus one of the colors of the two types of the charged pigment particles would be seen at the viewing side of the display cell.
The two types of electrophoretic display described above may involve vertical switching of the charged pigment particles. In other words, the charged pigment particles may be driven to move up and down, resulting in the charged pigment particles to be near or at either the top electrode plate or the bottom electrode plate.
An alternative driving mechanism involves lateral movement of the charged pigment particles. With this driving method, either the bottom of the display cell or the color of the solvent in which the charged pigment particles are dispersed will be exposed from the viewing side of the display cell. One of the disadvantages of the lateral switching method is that the colors displayed may appear washed-out under sun light, which would significantly impact on the quality of the images displayed.